This invention relates to devices for tensioning cords which are used to operate curtains, blinds or the like. Such cords are generally in the form of a suspended loop whereby pulling either run of the loop causes the curtains to be opened or closed or the blind to be raised or lowered as the case may be. Instead of allowing the loop to hang loosely, it has been the practice for ease of use and aesthetically to fix the loop to an adjacent edge or surface by means of a spring device which holds the cord taut.
According to the invention there is provided a cord tensioning device comprising a housing defining an elongate chamber, a carriage longitudinally slideable within the chamber, said carriage including a pulley around which said cord passes and a constant torque spring connected between said carriage and a wall of said chamber such that the carriage generates a substantially constant tension in the cord regardless of the position of the carriage in the chamber.
The use of a constant torque spring provides useful benefits over previous tensioners which incorporated tension springs. The tension in the cord remains constant wherever the tensioning device is secured. Fixing of the device is made easier because of the constancy of tension and the fact that only a small extension is needed to raise the tension to its constant value.